Phthalocyanine compounds are useful as coatings, printing inks, catalysts or electronic materials. In recent years, they have been extensively studied particularly for their use as electrophotographic photoreceptor materials, optical recording materials and photoelectric conversion materials.
It is known that phthalocyanine compounds generally exhibit several different crystal forms depending on the process of synthesis and the process of treatment and that the difference in crystal form has a great influence on their photoelectric conversion characteristics. For example, known crystal forms of copper phthalocyanine compounds include .alpha.-, .pi.-, .chi.-, .rho.-, .gamma.-, and .delta.-forms as well as a stable .beta.-form. These crystal forms are capable of interconversion by a mechanical strain, a sulfuric acid treatment, an organic solvent treatment, a heat treatment, and the like as described, e.g., in U.S. Pat. Nos. 2,770,629, 3,160,635, 3,708,292, and 3,357,989. Further, JP-A-50-38543 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") refers to the relationship between a crystal form of copper phthalocyanine and its electrophotographic characteristics. Besides copper phthalocyanine, it has been proposed to use various crystal forms of metal-free phthalocyanine, hydroxygallium phthalocyanine, chloroaluminum phthalocyanine, chloroindium phthalocyanine, etc. in electrophotographic photoreceptors.
In the course of study on the relationship between crystal forms of various phthalocyanine compounds and their electrophotographic characteristics, the present inventors previously discovered three novel crystal forms of chlorogallium phthalocyanine and revealed their excellent characteristics as a photoreceptor (as described in JP-A-5-98181).
Various processes for synthesizing chlorogallium phthalocyanine have hitherto been proposed. Known processes include, for example, (i) reaction between gallium trichloride and diiminoisoindoline (D.C.R. Acad. Sci., Vol. 242, p. 1026 (1956)), (ii) reaction between gallium trichloride and phthalonitrile (JP-B-3-30854; the term "JP-B" as used herein means an "examined published Japanese patent application"), (iii) reaction between gallium trichloride and phthalonitrile in butyl cellosolve in the presence of a catalyst (JP-A-1-221459); and (iv) reaction between gallium trichloride and phthalonitrile in quinoline (Inorg. Chem., Vol. 19, p. 3131 (1980)).
Where chlorogallium phthalocyanine is synthesized under a solvent-free condition as in processes (i) and (ii) above, there is a problem that the phthalocyanine ring undergoes chlorination, resulting in production of a mixture composed of gallium phthalocyanine compounds having different degrees of chlorine substitution, making it difficult to obtain a desired crystal form. Where synthesis is conducted by using a solvent, e.g., butyl cellosolve or quinoline, as in processes (iii) and (iv) above, the problem is that the solvent exerts a great influence on the electrophotographic characteristics of the resulting chlorogallium phthalocyanine, making it difficult to obtain a crystal form with desired electrophotographic characteristics.
The process proposed by the present inventors which comprises reacting gallium trichloride and diiminoisoindoline in quinoline (JP-A-5-98181) affords chlorogallium phthalocyanine having excellent electrophotographic characteristics in high yield. The chlorogallium phthalocyanine synthesized by this process has a stable crystal form showing an intense peak at a Bragg angle (28.+-.0.2.degree.) at 27.0.degree., which must be transformed to a crystal form suitable as an electrophotographic photoreceptor. When the crystal transformation is carried out by acid pasting which is one of widespread means for preparing phthalocyanine pigments, chlorogallium phthalocyanine undergoes hydrolysis. Therefore, the crystal transformation for obtaining a desired crystal form should be performed by first pulverizing by mechanical dry grinding to once decrease the crystallinity and then treating the fine powder with a solvent. However, not only does this process of crystal transformation attain very low efficiency but tend to cause pigment particles agglomerate to form bulky particles only to provide non-uniform crystals which hardly show stable characteristics.
Thus, the conventional processes of synthesis or treatment of chlorogallium phthalocyanine have encountered difficulty in obtaining a desired crystal form, or involved complicated operation for crystal transformation, or found difficulty in controlling a crystal form.